I just wanted to thank you for the wonderful body language breakdown, quite fascinating.
I always love a random "deep dip" into a science I know little about. Although I think we all know quite a lot about body language by default, it's mostly just a lack of skill to properly articulate what we perceive.
Especially mere description of body language is very hard for me to decode. If somebody asked me what "tightly clasped hands with interlocked fingers" meant I'd probably say something like "is that a thing you do when you try to maintain a dignified posture while sitting in a high-class restaurant?"
Yet when I saw her do it the meaning was pretty obvious to me. Or at least I felt it means what the body language expert said it means.
Anyways - to add my two bits, I think this definitely wasn't staged. Some think that being a seasoned actor automatically makes you able to pretend anything in real-time. But an actor has a role they project, script they adhere to, director and a whole team of people steering the action even though they might not intervene directly. It was a "scene" some, what, ten minutes long? If actors could shoot scenes 10 minutes per take, it wouldn't take months to record. Will's wife looks obviously offended the second she realizes what he said. And I am confident Will didn't hear or get the joke, his laugh seems to be one of those "hahaha I've no idea what he meant". Then he saw his wife and that probably triggered him connecting the dots.
Finally - do people know why the joke was so offensive? That she has a medical condition (alopecia) and her shaved head is by no means a choice? Kind of on its way to saying "hey there baldie" to a female cancer patient. Female baldness can be especially devastating and from the other reactions and the speech, it seems she has been a target of abuse for some time now. And he told that "joke" with a proud, arrogant stance which didn't help to tone down the emotional reaction either.
Addendum : I don't see that slap as a full-on act of agression─that would be the fist someone mentioned─but rather a "shame on you!" followed by a few assorted profanities. That's what makes me think of it as rather acceptable, unlike a punch or any sort of prolonged fighting.